![Texas Instruments SimpleLink Ethernet MSP432E401Y Technical Reference Manual Download Page 899](http://html1.mh-extra.com/html/texas-instruments/simplelink-ethernet-msp432e401y/simplelink-ethernet-msp432e401y_technical-reference-manual_1095578899.webp)
Functional Description
899
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
Ethernet Controller
Table 15-10. Enhanced Receive Descriptor 1 (RDES1) (continued)
Bit
Description
12:0
RBS1: Receive Buffer 1 Size
These bits indicate the first data buffer size in bytes. The buffer size must be a multiple of 4 even if the value of RDES2
(buffer 1 address pointer) is not aligned to the bus width. When the buffer size is not a multiple of 4, the resulting
behavior is undefined. If this field is 0, the DMA ignores this buffer and uses Buffer 2 or the next descriptor depending
on the value of RCH (Bit 14).
Table 15-11. Enhanced Receive Descriptor 2 (RDES2)
Bit
Description
31:0
Buffer 1 Address Pointer
These bits indicate the physical address of Buffer 1. The DMA uses the configured value for its address generation
when the RDES2 value is used to store the start of frame. The DMA performs a write operation with the RDES2[1:0]
bits as 0 during the transfer of the start of frame but the frame data is shifted as per the actual Buffer address pointer.
The DMA ignores RDES2[1:0] if the address pointer is to a buffer where the middle or last part of the frame is stored.
Note that buffers should be word-aligned.
Table 15-12. Enhanced Receive Descriptor 3 (RDES3)
Bit
Description
31:0
Buffer 2 Address Pointer (Next Descriptor Address)
These bits indicate the physical address of Buffer 2 when a descriptor ring structure is used. If the Second Address
Chained (RDES1[14]) bit is set, this address contains the pointer to the physical memory where the Next Descriptor is
present. If RDES1[14] is set, the buffer (Next Descriptor) address pointer must be bus word-aligned (RDES3[1:0] = 0)
However, when RDES1[14] is reset, there are no limitations on the RDES3 value, except for the following condition:
The DMA uses the configured value for its buffer address generation when the RDES3 value is used to store the start
of frame. The DMA ignores RDES3 [1:0] if the address pointer is to a buffer where the middle or last part of the frame
is stored.
Table 15-13. Enhanced Received Descriptor 4 (RDES4)
Bit
Description
31:15
Reserved
14
Timestamp Dropped
When set, this bit indicates that the timestamp was captured for this frame but got dropped in the RX FIFO because of
overflow.
13
PTP Version
When set, this bit indicates that the received PTP message uses the IEEE 1588 version 2 format. When reset, it uses
the version 1 format.
12
PTP Frame Type
When set, this bit indicates that the PTP message is sent directly over Ethernet. When this bit is clear and the message
type is non-zero, it indicates that the PTP message is sent over UDP-IPv4 or UDP-IPv6. The information about IPv4 or
IPv6 can be obtained from Bits 6 and 7.